This invention relates to easy-opening can ends and more particularly to an improved end structure for a container in which both the tear strip which defines the pour opening and the tab element used to rupture the scoreline forming the tear strip are retained on the end wall of the can end.
The ready acceptance of easy-opening cans has resulted in extended use of this type of container for a substantial number of can products, especially beverages such as beer, soft drinks and the like, and other products. Traditionally this type of container is in the form of an aluminum or other alloy can body which includes an end wall which is characterized by a lever or tab which is permanently joined to a tear strip, the latter being separable from the can top to provide a pouring spout, in the case of beverages, or to provide for removal of essentially the entire end wall of the container. In the form heretofore used, the end wall is ruptured along a continuous scoreline, and the pull tab, usually a ring tab, and tear strip are removed and normally discarded.
More recently, ecological concerns have resulted in container and end wall structures in which the tab and the tear strip remain attached to the container. Typical such structures are those described in U.S. Pat. Nos. 4,015,744; 4,024,981, and 4,030,631, all assigned to the present assignee. While the containers and easy-opening end structures and components thereof, as described in the above-identified patents, have been used in a significant number commercially, some users have objected because of the opening action in which the panel which forms the pour opening is forced into the can. While steps are normally taken during the packaging and shipment of containers of the type described to prevent accumulation of foreign matter on the surface of the container end wall, nonetheless, there have been some objections to easy-opening end structures in which the panel is forced into the container during the opening sequence.
A further problem which has arisen relates to some of the marketing approaches utilized in soft drink beverage marketing and other similar products. For example, various types of beverages are marketed in plastic or glass containers, the plastic or glass containers including a cap affixed to the container and which must be removed to gain access to the contents. In various promotional type marketing programs, the manufacturers have placed on the non-public side of the cap certain coded information usable in awarding prizes of various types from the manufacturer. Since the marking is on the non-public side, that is, the side of the cap facing the interior of the container and thus not visible until the cap is removed, the use of this type of marketing device has generally been limited to beverage container packages in which the consumer cannot inspect the non-public side of the closure element. As a matter of convenience, in easy-opening containers of the type identified in the preceeding patents, the consumer generally cannot see the non-public side of the pour panel which forms the pour opening since that panel is depressed into the container and it is inconvenient to remove the entire end wall of the container in order to determine what may be printed on the non-public side of the container end wall.
There are, in the prior art, easy-opening can ends which utilize a retained tear strip whose non-public side is exposed during an opening operation, see, for example, U.S. Pat. No. 3,900,128, also assigned to the same assignee as this application.
Another problem which sometimes exists with a retained tear strip end structure in which the tear strip is located above the end wall after rupture of the scoreline is "blow-off". It is believed that the sudden release of pressure during an opening sequence may cause the pour panel to be separated from the end wall.
In general, the approaches taken to prevent "blow-off" involve the provision of sufficient scoreline integrity to prevent the scoreline from being ruptured completely and instantaneously as a result of internal pressure of the container. However, the provision of scoreline integrity may also result in the need for increased force in order to achieve the initial pop, or initial fracture of the scoreline during an opening sequence. Generally, scoreline integrity may be achieved by providing a residual, which is higher than that normally used, with the result that it requires much more force to achieve an initial pop than would be the case with the same structure using a scoreline of a lesser residual. Also, when the residual is increased, in order to prevent "blow-off", it is generally necessary to use a tab of stronger or thicker stock material in order to withstand the forces in bending to which the longitudinal tab lever is subjected during the initial pop and tearing or severance of the scoreline.
The structure described in U.S. Pat. No. 3,900,128 is satisfactory as an end wall structure and does solve some of the problems above described. However, the ends thereof did not stack as well as some of the other goods heretofore used. More particularly, in the automated equipment generally used in the beverage field, the end walls are advanced to an appropriate station where they are double-seamed on the can end and the transport of the can end structures from one point to the other generally requires that they "stack" properly in order to be moved from one point to another by automated equipment.
Since the operation of can ends having a retained tear strip results in the tear strip being above the end wall of the container and folded back during an opening sequence, provisions have also been made to reduce the sharpness of the metal along the edges of the tear strip in order to reduce laceration.
Still another problem, as discussed in U.S. Pat. No. 3,900,128 is that of raising the end of the tab above the end wall and possibly above the chime as a result of doming.
Another problem which has arisen, especially with beer and beverage containers is buckling of the end wall. In part, this problem has been exacerabated by the tendency to go to thinner end wall stock for reasons of economy. As understood, if the internal pressure within the packed container increases an appreciable amount, as may occur during shipment or storage in hot climates or seasons, the end wall literally buckles such that a portion of the end wall is deformed upwardly above the top of the end flange. In those instances in which the rivet is closer to the chuck wall than to the center of the end, the buckling appears to be generated along the region between the chuck wall and the rivet.
Prior art attempts to reduce buckling have involved coining what is called the panel radius, i.e. that region of the end wall which is effectively the outer radial edge of the center panel of the end. The coined band extends 360 degrees around the center panel and may be formed on the public or non-public side of the end. This coined panel radius has been effective in reducing buckling by uniformly strengthening the end wall.
If, however, the structure of the end is non-symmetrical, i.e. the rivet is not centered in the end panel or there are formations in the end panel which significantly effect end symmetry, the 360 degree coined panel radius is not fully effective to prevent buckling in an unwanted region. For example, if there is a finger well under the lifting end of the tab, buckling may take place in the region of the finger well. So too, if the scoreline is adjacent to the radial edge of the panel radius, buckling may take place in that region of the end wall. More specifically, if both the rivet and the scoreline are off center and adjacent to the radial edge of the panel, it has been observed that in those instances in which buckling takes place, it may be sufficiently severe to cause rupture of the scoreline. Thus, while buckling is a problem, it is even a greater problem when it occurs in a region of the end where it affects operation or integrity of the end structure.
Accordingly, it is desirable to provide an easy-opening end structure for use as a closure member in a can such that there is a retained strip whose non-public side is exposed on rupture of the principal scoreline, and preferably a structure which reduces lacerations. It is also advantageous to provide an easy-opening end in which all components of the end structure remain with the end structure, thus eliminating loose pieces which may become litter and thus solving, to some extent, concerns related to the ecology and the litter which may accumulate from indiscriminantly-disposed-of tear strips. It is also advantageous to provide an ecology-type of easy-opening end structure in which the tab is in the form of a pull-ring of the type used for many years in easy-opening end structures, and whose basic opening sequence is similar to that of the pull-ring type of easy-opening ends used for many years but which involved separating both the tab and the tear strip from the end structure. Further, it is desirable to provide a structure of the type described in which the tendency of the lifting end of the tab to be displaced upwardly as a result of doming of the end wall is reduced.